LTE (Long Term Evolution) and LTE-A (Long Term Evolution-Advanced) standards define terminal (User Equipment) categories, such as a terminal category 1, a terminal category 2, . . . , and a terminal category 10. Different terminal categories correspond to different uplink capabilities and different downlink capabilities.
For example, a downlink capability of the terminal category 1 includes the maximum number of downlink shared channel DL-SCH transport block bits received within a TTI (Transmission Time Interval) is 10296 bits; the maximum number of bits of a downlink shared channel DL-SCH transport block received within a TTI is 10296 bits; the total number Nsoft of soft channel bits is 250368 bits; and the maximum number of supported layers for spatial multiplexing in downlink is 1 layer.
An uplink capability of the terminal category 1 includes the maximum number of uplink shared channel UL-SCH transport block bits transmitted within a transmission time interval TI is 5160 bits; the maximum number of bits of an uplink shared channel UL-SCH transport block transmitted within a TTI is 5160 bits; and support for 64QAM in uplink is no.
The total number Nsoft of soft channel bits in the downlink capability of the terminal category represents a capability of processing a HARQ (Hybrid Automatic Repeat Request) by a terminal, and determines that the terminal has a buffer that can store Nsoft bits. The number of soft channel bits that can be occupied by each parallel downlink HARQ process is a part of the Nsoft, and a corresponding buffer is used to temporarily store soft channel bits corresponding to the HARQ process.
In an actual application, a transport block first undergoes channel coding before being transmitted. If a transport block is too long (the number of information bits input by coding exceeds 6144), the transport block is divided into multiple code blocks, where each code block includes redundant bits in addition to information bits after undergoing channel coding at a ⅓ bit rate. When a terminal receives a transport block that is transmitted for the first time, the terminal attempts to decode received data. If the data of the transport block is decoded successfully, the successfully decoded data is submitted to a higher layer for further processing; if the data of the transport block fails to be decoded, the terminal replaces data stored in a buffer corresponding to a HARQ process with the data that the terminal is attempting to decode. When the terminal receives a transport block that is retransmitted, retransmitted data of the transport block is combined with the data of the transport block currently in the buffer corresponding to the HARQ process, and the terminal attempts to decode combined data. If the data of the transport block is decoded successfully, the successfully decoded data is submitted to the higher layer for further processing; if the data of the transport block fails to be decoded, the terminal replaces the data that the terminal is attempting to decode, with the data stored in the buffer corresponding to the HARQ process.
A transport block first undergoes channel coding before being transmitted. If a transport block is too long, the transport block is divided into multiple code blocks, where the number of corresponding code words is C, that is, a transport block is divided into C code blocks. Then, a soft buffer size corresponding to each code block is Ncb=NIR/C. Because for a same transport block, a redundancy version used for data retransmission is different from that used for last transmission of the transport block, bit selection needs to be performed during rate matching that is performed before each code block is transmitted, and then selected bits are used to transmit the code block.
Currently, during transmission of a downlink transport block, when each code block included in the downlink transport block is transmitted, a formula 1 is used to determine a soft buffer size corresponding to an rth code block:
                              N          cb                =                  min          ⁡                      (                                          ⌊                                                      N                    IR                                    C                                ⌋                            ,                              K                w                                      )                                              (                  formula          ⁢                                          ⁢          1                )            
where the Ncb is a soft buffer size of a code block;
the NIR is a soft buffer size of a transport block, and is calculated by using a formula 2;
the C is the number of code blocks;
the Kw is a length of a virtual circular buffer of the rth code block; and
                              N          IR                =                  ⌊                                    N              soft                                                      K                C                            ·                              K                MIMO                            ·                              min                ⁡                                  (                                                            M                                              DL                        ⁢                        _                        ⁢                        HARQ                                                              ,                                          M                      limit                                                        )                                                              ⌋                                    (                  formula          ⁢                                          ⁢          2                )            
where the KC is the maximum number of carriers supported during carrier aggregation; if a terminal category of a terminal is 8, and Nsoft=35982720, then KC=5; if a terminal category of a terminal is 6 or 7, Nsoft=3654144, and a capability of the terminal is that the maximum number of supported layers for spatial multiplexing in downlink is 2, then KC=2; in other cases except the foregoing cases, KC=1. The KMIMO is a parameter related to a configured transmission mode, and represents the number of transport blocks that can be transmitted simultaneously within a TTI; if the terminal is configured to receive data transmitted on a PDSCH (Physical Downlink Shared channel) based on a transmission mode 3, 4, 8, 9, or 10, KMIMO=2; in other cases, KMIMO=1. The MDL_HARQ is the maximum number of downlink HARQ processes of a terminal in each serving cell; during downlink reception, the terminal has a HARQ entity for processing several parallel HARQ processes for each serving cell, and each downlink HARQ process corresponds to a HARQ process ID; the maximum number of downlink HARQ processes corresponding to each HARQ entity is 8 in an FDD (Frequency Division Duplex) system; the maximum number of HARQ processes in a TDD (Time Division Duplex) system is related to a UL (Uplink)/DL (Downlink) configuration, for example, when the UL/DL configuration is 0, the maximum number of HARQ processes is 4, when the UL/DL configuration is 1, the maximum number of HARQ processes is 7, when the UL/DL configuration is 2, the maximum number of HARQ processes is 10, when the UL/DL configuration is 3, the maximum number of HARQ processes is 9, when the UL/DL configuration is 4, the maximum number of HARQ processes is 12, when the UL/DL configuration is 5, the maximum number of HARQ processes is 15, and when the UL/DL configuration is 6, the maximum number of HARQ processes is 6; in addition, whether in the FDD or TDD system, the terminal further has an additional dedicated broadcast HARQ process. The Mlimit is a limit value used when a transmit end determines a buffer size that can be used by each HARQ process of a terminal; for example, when the TDD UL/DL configuration is 0, the maximum number of HARQ processes of the terminal is 4, and therefore, the transmit end calculates the buffer size that can be used by each HARQ process of the terminal according to 4 HARQ processes; when the TDD UL/DL configuration is 5, the maximum number of HARQ processes of the terminal is 15, and therefore, the transmit end calculates the buffer size that can be used by each HARQ process of the terminal according to 8 HARQ processes.
However, when the formula 1 is used to select the Ncb corresponding to downlink data, and broadcast data (including an SI (System Information) message, an RAR (Random Access Response) message, and a Paging message) is transmitted, there is a disadvantage that the terminal cannot perform decoding correctly because an information sequence transmitted by a base station and an information sequence that the terminal expects to receive are inconsistent. A reason is as follows.
The Nsoft of some terminals is 25344, and the NIR obtained by calculation according to the formula 2 is 3168 bits (where MDL_HARQ=8, assuming that KC=1 and KMIMO=1 and using the FDD system as an example). For example, when the number of broadcast transport block TB bits is 2216, Kw=6816, and C=1. Therefore, when downlink data is data that is delivered over a PCH (Paging Channel) to a physical layer, or is data that is delivered over a DL-SCH (Downlink Shared Channel) associated with an RA (Random Access)-RNTI (Radio Network Temporary Identifier) to a physical layer, or is data that is delivered over a DL-SCH associated with an SI (System Information)-RNTI to a physical layer, the base station may select a parameter
      N    cb    =            min      ⁡              (                              ⌊                                          N                IR                            C                        ⌋                    ,                      K            w                          )              =                  ⌊                              N            IR                    C                ⌋            =      3168      when performing bit selection. For terminals of terminal categories 1 to 10, the base station may select a parameter
      N    cb    =            min      ⁡              (                              ⌊                                          N                IR                            C                        ⌋                    ,                      K            w                          )              =                  K        w            =      6816      when performing bit selection. Therefore, no matter which parameter is selected by the base station to perform bit selection and transmit broadcast data, a case in which assumptions of some terminals and the base station are inconsistent may occur. For example, when the base station selects the parameter Ncb=3168, the terminals of the terminal categories 1 to 10 may receive the broadcast data according to the parameter Ncb=6816; when the base station selects the parameter Ncb=6816, a terminal whose Nsoft is 25344 may receive the broadcast according to the parameter Ncb=3168. In the case of inconsistent assumptions of the terminal and the base station, information bits that the terminal expects the base station to transmit are not information bits actually transmitted by the base station, and therefore, there is the disadvantage that the terminal cannot perform decoding correctly.